To achieve a lighter and thinner touch display panel, the research on integrations of touch panel and liquid crystal display panel becomes popular. Among others, the In-Cell touch solution in which a touch function is embedded into the liquid crystal display panel has been widely concerned. The In-Cell touch solution generally includes a self-capacitive solution and a mutual-capacitive solution.
Specifically, as for a liquid crystal display panel with an advanced super dimension switch (ADSDS) mode, the self-capacitive In-Cell touch solution is as follows: as shown in FIG. 1, a metal layer serving as a common electrode in the liquid crystal display panel is divided into several blocks (i.e., electrode blocks) insulated from each other and serving as touch sensor units, and the touch sensor units are connected to a driving IC through specific metal wires. When the liquid crystal display panel is touched by a finger, the capacitance value of a touch sensor unit at a position corresponding to the touch is changed (or, the voltage value of the common electrode at the position is changed), and the driving IC detects the change of the capacitance value to determine the touched position, thereby achieving the touch control function.
It is necessary to perform an electric test (ET) on a touch display panel so as to ensure product quality. For simplification of structure and improvement of test efficiency, a method in which an electric test on display function and touch control function of a touch display panel is performed though a single structure has been proposed currently. The existing ET structure, however, can only simultaneously apply a same test signal to all touch sensor units by controlling test switches, and thus cannot test the short defect between different touch sensor units. Moreover, when the open defect occurs for a touch sensor unit, the touch sensor unit is in a floating state in which the test signal cannot be applied thereto, and has a small uncertain voltage close to an initial zero potential. Therefore, in a case where a test on the display function of the touch display panel is performed and the applied test signal has a voltage value of 0 V, although there may be a difference in brightness between a display area corresponding to the touch sensor unit (which has the open defect) and a display area corresponding to other touch sensor unit in a normal state, such difference in brightness may be too small to be recognized by human eyes, which finally results in that the possibly existing open defect cannot be detected.
Moreover, the self-capacitive In-Cell design requires the use of expensive Touch & Display Driver IC (TDDI) components. Therefore, it is necessary to improve detection rate of defects for the touch display panel as high as possible before the assembling process, so as to reduce, to the largest extent, loss of materials (particularly, loss of the TDDI components) in the assembling process due to the defect of the touch display panel.
However, the ET solutions designed for the existing ADSDS-type self-capacitive touch display panels cannot detect the short defect between different touch sensor units, and cannot ensure that the open defects of the touch sensor units have been completely detected. As a result, the test results are not accurate, and the detection rate of the defective products is low. If the touch display panel having defects is transferred to the assembling stage, a large amount of materials such as polarizers POL, driving ICs and flexible printed circuits FPCs may be lost, and the production costs may be increased. Thus, there needs a technical solution by which the open or short defect of a touch display panel can be accurately tested so as to improve the test accuracy, improve the detection rate of defective products and lower the production costs.